A Technology for Enhanced Control of Erosion, Sediment and Metal Leaching at Disturbed Land Using Polyacrylamide and Magnetite Nanoparticles

Transcription

1 A Technology for Enhanced Control of Erosion, Sediment and Metal Leaching at Disturbed Land Using Polyacrylamide and Magnetite Nanoparticles Min Zheng and Dongye Zhao Environmental Engineering Program Department of Civil Engineering Auburn University, Auburn, AL /11/2016

2 Overview Outline Part I: Soil erosion tests with simulated rainfall Part II: Aqueous phase arsenate immobilization batch tests Part III: Immobilization of arsenate at disturbed surface soils in box tests Conclusions 2

3 Outline Overview Part I: Soil erosion tests with simulated rainfall Part II: Aqueous phase arsenate immobilization batch tests Part III: Immobilization of arsenate at disturbed surface soils in box tests Conclusions 3

4 Soil erosion Ø One of the most serious ecoenvironmental problems in the world. Ø Construction sites and other locations with disturbed soil are susceptible to soil erosion; Ø There is a marked relationship between rainfall and erosion, which accelerates soil degradation; Ø Soil is quite vulnerable on steep sloping island, which can cause nutrient loss and metal leaching. Vulcan Quarry site soil erosion view 4

5 Problems associated with soil erosion Soil erosion Releases of large quantities of fine sediments Toxic metals leaching 5

6 Rules and regulations Federal environmental laws Clean Air Act (CAA) (1990) Clean Water Act (CWA) (1987) National Pollutant Discharge Elimination System (NPDES) permit Phase I (1990) Phase II NPDES (2003) U.S. EPA construction sites effluent limitation guidelines 6

7 U.S. EPA construction sites effluent limitation guidelines To control erosion and sediment release, operators of regulated sites are required to develop and implement storm water pollution prevention plans and to obtain the required permits from an authorized state agency or from the US EPA. The effluent limitation guidelines proposed by US EPA for initial turbidity was evolved as follows: In 2008, 13 NTU In 2011, 280 NTU In 2014, No-numeric limitation 7

8 Polyacrylamide (PAM) application: PAMs have been used in the US since 1995 for reducing irrigation-induced erosion and for enhancing infiltration, it can also greatly improve runoff water quality by reducing the presence of sediments, N, P, COD (chemical oxygen demand), pesticides, weed seeds, and microorganisms. In 2000, National Resources Conservation Service specified soil treated with anionic PAM as a Best Management Practice (BMP) for controlling soil erosion. 8

9 Polyacrylamides (PAMs) Ø Formed from acrylamide subunits; Ø One in five chain segments provide a charged site; Ø Large (12-15 megagrams per mole) water soluble (non-cross-linked) anionic molecules, containing <0.05% acrylamide monomers; Ø Aggregate fine soil particles through Coulombic and Van der Waals forces; Ø Optimum application rate of PAM is influenced by soil slope; Ø Anionic PAMs are safe and environmentally friendly; Ø Cost between $4.50 to $12 per kg active ingredient. PAM polymer structure subunit (Sojka et al., 2005) Granular Anionic PAM 9

10 Limitations of PAM Anionic PAMs are negatively charged, the effectiveness is greatly reduced for binding with soil particles or colloids that carry similar negative surface charges; Less effective for soils of low metal or clay/silt content (e.g. sandy soils), and it often fails to bind with soils of high organic matter (OM); PAM of high MW would penetrate poorly into aggregates with a less effective depth, greater viscosity can induce reduction of soil hydraulic conductivity; Little is known about its effectiveness on very steep slopes (4:1 to 2:1); Anionic PAMs carry amide and carboxylic functional groups, both of these can interact with metal cations such as Pb 2+. However, there has been no documented research on its effectiveness for retaining metals or metal oxyanions in runoff. 10

11 Arsenic and soil erosion Arsenic is an oxyanion (HAsO 4 2- ), one of WHO s 10 chemicals of major public health concern; Abandoned mines may act as major sources of arsenic contamination to the nearby environment; Soil functions as an important sink for arsenic, soil sorbed arsenic is sensitive to mobilization due to weathering, soil erosion, and human actions; Soil erosion contributed 2.38x 10 8 kg per year of dissolved and suspended arsenic to the oceans; Iron-based arsenic removal technologies make use of the strong binding between iron and arsenate; Magnetite nanoparticles offer strong affinity for arsenate. 11

12 Hypotheses Limitation of PAM Modify PAM using magnetite nanoparticles will alter PAM molecular size and structure without increasing its viscosity. PAM performance on steeper slope NP-modified PAM will work more effectively, especially for steep (3:1) slope for controlling both erosion and metal leaching PAM effectiveness for retaining arsenic in runoff. Arsenate will be used as a model metalloid Magnetite nanoparticles can immobilize arsenic leached from eroded soil under various conditions 12

13 Outline Overview Part I: Soil erosion tests with simulated rainfall Part II: Aqueous phase arsenate immobilization batch tests Part III: Immobilization of arsenate at disturbed surface soils in box tests Conclusions 13

14 Ø Soils Materials and methods v Vulcan Site Soil (Vulcan Materials Company s Quarry site, Notasulga, AL) v Smith Farm Soil (Auburn University E.V. Smith Research Farm, Shorter, AL ) 14

15 Table 1 Selected Physical and Chemical Properties of the 15 Studied Soils Vulcan Site Soil Smith Farm Soil ph Organic Matter (%) CEC a (meq/100g) Fe (mg/l) Al (mg/l) Ca (mg/l) Mg (mg/l) P (mg/l) 9 3 Mn (mg/l) Sand (%) Silt (%) Clay (%) Texture Class Sandy Loam Loam PZC

16 Simulated rainfall test procedure STEP 1 Soil compaction and then apply various treatments STEP 2 Simulated Rainfall test setup (12*36*3 in) STEP 3 3:1 slope STEP 4 Simulated Rainfall tests for 60 mins PAM PAM+NP STEP 5 Runoff parameters measurement (Weight, volume, initial turbidity, turbidity kinetics and weight of sediment) 16

17 Statistical analysis Statistical analysis on the experimental data was carried out by using Statistical Analysis System (SAS) or Microsoft Excel. All the results were expressed as means ± S.D. (standard deviation) of replicates when possible. Experimental results under various conditions were analyzed by one-way analyses of variance (ANOVA) or t-test to compare the differences. Differences were considered significant at p <

18 Results Vulcan site soil v Average runoff concentration 100 v Initial runoff turbidity 1000 Runoff Concentration (g/l) Bare Vulcan Soil 0.3% PAM 705 Treated 0.3% PAM 705 Stabilized 0.1g/L Fe NPs Treated Runoff Turbidity (NTU) Bare Vulcan Soil 0.3% PAM 705 Treated 0.3% PAM 705 Stabilized 0.1g/L Fe NPs Treated Time (mins) Time (mins) Figure 2.14 Comparison of Bare and Treated Vulcan Site Soils Runoff Concentration Variation with Time Figure 2.15 Comparison of Bare and Treated Vulcan Site Soils Runoff Turbidity Variation with Time Average runoff concentration reduction Initial runoff turbidity reduction PAM % 89% PAM NPs 90.8% 83% 18

19 100 v Turbidity kinetics 1000 Turbidity (NTU) PAM 0.3 8h 1 min 5 min 10 min 15 min 20 min 25 min 30 min 35 min 40 min 45 min 50 min 55 min 60 min Turbidity (NTU) Bare 96h Time (h) 1 min 5 min 10 min 15 min 20 min 25 min 30 min 35 min 40 min 45 min 50 min 55 min 60 min Figure 2.16 Bare Vulcan Site Soil Thirteen Points Runoff Samples Turbidity Variation with Time Turbidity (NTU) Time (h) Figure % PAM705 Treated Vulcan Site Soil Thirteen Points Runoff Samples Turbidity Variation with Time PAM NPs 48h 1 min 5 min 10 min 15 min 20 min 25 min 30 min 35 min 40 min 45 min 50 min 55 min 60 min Time (h) Figure % PAM705 Stabilized Magnetite Nanopartilces(total Fe= 0.1g/L) Treated Vulcan Site Soil Thirteen Points Runoff Samples Turbidity Variation with Time

20 Smith Farm soil v Average runoff concentration v Initial runoff turbidity Runoff Concentration(g/L) Bare Soil 0.25% PAM 705 Treated 0.3% PAM 705 Treated 0.3% PAM 705 Stabilized 0.1g/L Fe Magnetite NPs Initial Turbidity (NTU) Bare Vulcan Soil 0.25% PAM705 Treated 0.3% PAM705 Treated 0.3% PAM705 Magnetite NP Treated Time (mins) Figure 2.20 Comparison of Bare and Treated Smith Farm Soil Runoff Concentration Variation with Time Time (mins) Figure 2.21 Comparison of Bare and Treated Smith Farm Soils Runoff Turbidity Variation with Time Average runoff concentration reduction Initial runoff turbidity reduction PAM % 95.6% PAM 0.3 ~100% 98.6% PAM NPs 89.1% 90.5% 20

21 100 v Turbidity kinetics Turbidity (NTU) PAM h 1 min 5 min 10 min 15 min 20 min 25 min 30 min 35 min 40 min 45 min 50 min 55 min 60 min Turbidity (NTU) Bare 17d Time (h) 1 min 5 min 10 min 15 min 20 min 25 min 30 min 35 min 40 min 45 min 50 min 55 min 60 min Figure 2.22 Bare Smith Farm Soil Thirteen Points Runoff Samples Turbidity Variation with Time Turbidity (NTU) Time (h) Figure % PAM705 Treated Smith Farm Soil Thirteen Points Runoff Samples Turbidity Variation with Time PAM NPs 4h 1 min 5 min 10 min 15 min 20 min 25 min 30 min 35 min 40 min 45 min 50 min 55 min 60 min Ø The initial turbidity for 0.3% PAM 705 treated group was below 13NTU Time (h) Figure % PAM705 Stabilized Magnetite Nanopartilces(Total Fe= 0.1g/L) Treated Smith Farm Soil Thirteen Points Runoff Samples Turbidity Variation with Time 21

22 Outline Overview Part I: Soil erosion tests with simulated rainfall Part II: Aqueous phase arsenate immobilization batch tests Part III: Immobilization of arsenate at disturbed surface soils in box tests Conclusions 22

23 Materials and Methods Ø Batch equilibrium adsorption tests were performed in duplicate. First, the particles were prepared at 0.1 g/l as total Fe with 0.3 wt.% PAM, or 0.1 g/l Fe with 0.04, 0.1 wt.% of starch in 30 ml plastic vials. Ø The were then mixed with 1 ml arsenate stock solution, which yielded an initial arsenic concentration of mg/l. The systems were equilibrated on a rotating rack (40 rpm) for 12 days. Ø At equilibrium, the suspension was filtered through a µm membrane filter. The filtrate was then acidified with 5% nitric acid, and then analyzed for total As in the aqueous phase. 23

24 Results and Discussion Table 2 Arsenate removal (%) by 3 kinds of NPs NP Names Arsenate Removal (%) 0.04S 0.1Fe NPs S 0.1Fe NPs 98.0 Fig. 7 Aqueous phase arsenic removal by magnetite nanoparticles of 0.1g/L total Fe coated with: (i) 0.04 wt.% starch,(ii) 0.1 wt.% starch and (iii) 0.3 wt.%pam. Error bars indicate standard error. 0.1Fe 0.3PAM NPs

25 Outline Overview Part I: Soil erosion tests with simulated rainfall Part II: Arsenate adsorption and immobilization batch tests Part III: Immobilization of arsenate at disturbed surface soils in box tests Summary of conclusions 25

26 Materials and methods (a) Compacted soil with 4x4x1 (in) removed; (b) Fill the space with NP- Amended Arsenate Contaminated Soils; (c) Apply PAM 705; (d)test Plots Under Rain Simulation Event. 26 Ø The box was loaded with 2- inch the soils; Ø The 4x4x1 (in) at the center was removed and replaced with arsenate laden soils Ø Spray 0.3% PAM705 (w/w) 260ml to the test plot in the following day and let it dry for 3 days; Ø During a simulated rainfall event, runoff samples were collected every 5 minutes for 60 minutes. Ø The samples were then filtered with 25nm membrane filter and filtrates were analyzed for total As and Fe concentration.

27 Results and discussion Arsenic immobilization in box test As(V) mass( µ g) Control Treated w/ 0.5g total Fe Magnetite (ph= 6.65) Treated w/ 0.5g total Fe Magnetite (ph= 5.46) Treated w/ 1g total Fe Magnetite (ph= 6.95) As(V) Mass( µ g) Control 0.5g Total Fe Treated (ph = 7.04) 1g Total Fe Treated (ph = 6.65) 1g Total Fe Treated (ph = 5.46) Experiment Duration(mins) Figure 4.2 Runoff As(V) Mass in Three Magnetite Nanoparticles Treated As(V) Ladened Vulcan Site Soil Experiment Duration (mins) Figure 4.3 Runoff Arsenate Mass in Three Magnetite Nanoparticles Treated Arsenate Landed Smith Farm soil 27

28 Outline Overview Part I: Soil erosion tests with simulated rainfall Part II: Aqueous phase arsenate immobilization batch test Part III: Immobilization of arsenate at disturbed surface soils in box tests Conclusions 28

29 Conclusions PAM stabilized magnetite nanoparticles (Total Fe=0.1g/L) reduced runoff erosion (soil mass) by 90.8% for Vulcan Site soil and 89.1% for Smith Farm soil, and turbidity by % for the two soils, with 30% reduction of viscosity compared to PAM only. Starch bridged magnetite nanoparticles combined with PAM application successfully immobilized arsenate in soils ( less than 1.2% arsenate was leached). Vulcan site soil is more vulnerable to runoff, but more responsive to the treatment compared to Smith Farm soil. ph, dosage of Fe nanoparticles and soil texture can affect arsenate immobilization. NP-modified PAM may simultaneously control erosion and metals leaching 29

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